Centrifugal Compressor

ABSTRACT

A centrifugal compressor of the present invention can be operated without degrading the efficiency of the impeller or reducing the operating range thereof even when the centrifugal compressor is operated in an environment in which a liquid likely mixes. A centrifugal compressor of the present invention includes a rotating shaft which rotates rotationally, and an impeller including a hub fixed to the rotating shaft and plural vanes fixed to the hub at a predetermined interval in a circumferential direction. The centrifugal compressor compresses a fluid by rotation of the impeller. The hub includes plural through holes penetrating the hub from a front side to a rear side of the impeller.

FIELD OF THE INVENTION

The present invention relates to a centrifugal compressor, particularly a centrifugal compressor suitable for use in gas fields yielding natural gas.

BACKGROUND OF THE INVENTION

In conjunction with the increase in demand for fossil fuel and the advancement of extracting technologies, development is recently shifting from conventional gas fields to non-conventional gas fields. As a result, it is necessary to install compressors in severe environments, such as under very deep seas and directly below gas fields.

To extract natural gas from under very deep seas, a method is considered in which a compressor (subsea compressor) is installed on the sea bottom several hundred meters deep and natural gas is pressure-fed from an underground reservoir. To extract natural gas from directly below gas fields, a method is proposed in which a compressor is installed in a gas well several thousand meters underground and gas is compressed on the bottom of the well and fed onto the ground. For this purpose, research and development are being conducted on compressors (downhole compressors).

In the initial phase, the underground pressure is high but the internal pressure is reduced as gas is extracted. As long as the underground pressure of a gas field is high, it is possible to let natural gas flow to the ground by itself. When the pressure is reduced to a limit or below, gas cannot flow to the ground by itself any longer. For this reason, a gas well with a reduced pressure is conventionally considered as being exhausted.

However, even after the underground pressure is reduced to a level insufficient to let gas flow by itself, a considerable quantity of natural gas remains in the gas field.

Consequently, it is considered that the production capacity of a gas field can be recovered by using a downhole compressor to boost the pressure directly below the gas field.

Since the above-mentioned subsea compressors and downhole compressors are installed on the bottom of a gas field or directly below a gas field, they are operated in very severe environments.

In general, the working fluids for compressors used in gas fields yielding natural gas include not only natural gas but also liquid containing water and soft liquid hydrocarbons called condensate. These compressors are placed in an operating environment in which the liquid is mixed. Especially, under a very deep sea or directly below a gas field mentioned above, compressors are exposed to an environment with a very high rate of the liquid.

A liquid that entered inside a compressor in such an environment is considered to cause various problems, including degradation in efficiency due to collision with an impeller, the narrowing of an operating range and the production of unstable fluid force due to the block of a flow path caused by fouling, and the reduced thickness of an impeller due to erosion. Therefore, compressors used in gas fields yielding natural gas require a technology to operate the compressor without degrading the performance thereof in an operating environment in which the liquid is prone to mix.

Conventional technologies of compressors that cope with the above problems are disclosed in Documents 1 and 2.

Document 1 discloses that grooves are formed in the surface of a vane of an impeller and the grooves are utilized to flow a fluid outward in the radial direction, the fluid having flowed in from the direction of a rotating shaft.

Document 2 discloses that grooves are extended from an inlet area to an outlet area such that a fluid flows from the inlet area outward in the radial direction with the rotation of an impeller disk.

Document 1: JP 2014-141909

Document 2: JP 2003-511596

In the technologies disclosed in Documents 1 and 2, although the installation of grooves makes the fluid flow easily, the fluid remains inside the compressor and is likely to attach to the impeller and, therefore, the problems have not been solved fundamentally yet.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the foregoing problems. An object of the present invention is to provide a centrifugal compressor that can be operated without degrading the efficiency of the impeller or reducing the operating range thereof even when the centrifugal compressor is operated in an environment in which a liquid likely mixes.

To achieve the above object, a centrifugal compressor of the present invention includes a rotating shaft which rotates rotationally, and an impeller including a hub fixed to the rotating shaft and a plurality of vanes fixed to the hub at a predetermined interval in a circumferential direction, wherein the centrifugal compressor compresses a fluid by rotation of the impeller, and wherein the hub includes a plurality of through holes penetrating the hub from a front side to a rear side of the impeller.

The present invention brings about an effect of providing a centrifugal compressor that can be operated without degrading the efficiency of the impeller or reducing the operating range thereof even when the centrifugal compressor is operated in an environment in which a liquid likely mixes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the upper half of a centrifugal compressor according to a first embodiment of the present invention;

FIG. 2 is a perspective view of the upper half of a centrifugal compressor according to the first embodiment of the present invention;

FIG. 3 is a sectional view illustrating the position of a through hole in a centrifugal compressor according to the first embodiment of the present invention;

FIG. 4 is a sectional view of the upper half of a centrifugal compressor according to a second embodiment of the present invention;

FIG. 5 is a perspective view of the upper half of a centrifugal compressor according to the second embodiment of the present invention;

FIG. 6 is a sectional view illustrating the position of a through hole in a centrifugal compressor according to the second embodiment of the present invention;

FIG. 7 is a sectional view of the upper half of a centrifugal compressor according to a third embodiment of the present invention; and

FIG. 8 is a sectional view of the upper half of a conventional centrifugal compressor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, a description will be given to a centrifugal compressor according to embodiments of the present invention with reference to the drawings. Through the following description of the embodiments, identical components will be indicated with identical reference characters.

First Embodiment

FIG. 1 and FIG. 2 illustrate a centrifugal compressor 1 according to a first embodiment of the present invention.

As illustrated in FIG. 1 and FIG. 2, the centrifugal compressor 1 of this embodiment, which is a turbo centrifugal compressor, includes a rotating shaft 11 which rotates rotationally and an impeller 10 having a hub 14 fixed to the rotating shaft 11 and plural vanes 12 fixed to the hub 14 at substantially equal intervals, each of which is a predetermined interval, in the circumferential direction. In this embodiment, the hub 14 includes plural through holes 15 penetrating the hub 14 from the front side (left side of FIG. 1) to the rear side (left side of FIG. 1) of the impeller 10. In addition, as illustrated in FIG. 3, the through holes 15 are located between the outside diameter R_(h) of the hub 14 and the outside diameter R_(sh) of the shroud 13 of the vanes 12.

As illustrated in FIG. 2, the through holes 15 are provided in the hub 14 between the plural vanes 12 on the rotating shaft 11 side such that the through holes 15 penetrate the hub 14 from the front side to the rear side of the impeller 10. (That is, the through holes 15 penetrate the hub 14 from the front side to the reverse side of the paper of FIG. 2.)

In the configuration of this embodiment, a working fluid sucked from a suction port (located on the left side of FIG. 1) by the rotation of the impeller 10 is increased in speed and pressure by the centrifugal action of the impeller 10. The working fluid is then guided to the downstream side.

When a conventional centrifugal compressor 1, shown in FIG. 8, is operated in an environment in which the liquid is mixed, the liquid that entered the impeller 10 once attaches to the hub 14 in the usual case. If the liquid attaches to the vanes 12 through the hub 14, the shaft power of the impeller 10 is increased and thus the efficiency of the centrifugal compressor 1 is degraded. Since droplets attached to the vanes 12 and the hub 14 block the flow path, the operating range is narrowed and unstable fluid force is produced. Further, the reduced thickness of the impeller 10 due to erosion is brought about.

In the above-mentioned configuration in this embodiment, the liquid that flowed into the impeller 10 is about to attach to the hub 14 but almost all the droplets are discharged to the rear side of the impeller 10 through the through holes 15 formed between the position of the outside diameter R_(h) of the hub 14 and the position of the outside diameter R_(sh) of the shroud 13. This makes it possible to prevent the liquid from attaching to the vanes 12 and suppress degradation in the efficiency due to increase in the shaft power of the impeller 10. Since attaching of the droplets to the vanes 12 and the hub 14 is suppressed, it is possible to suppress the narrowing of the operating range and the production of unstable fluid force due to the block of the flow path.

Therefore, by forming the plural through holes 15 penetrating the hub 14 from the front side to the rear side of the impeller 10 as in this embodiment, even when the centrifugal compressor 1 is operated in an environment in which the liquid is mixed, droplets that entered the impeller 10 can be efficiently removed and the compressor 1 can be operated without degrading the efficiency of the impeller 10 or narrowing the operating range thereof.

Second Embodiment

FIG. 4 and FIG. 5 illustrate a centrifugal compressor 1 according to a second embodiment of the present invention.

The configuration of the centrifugal compressor 1 according to this embodiment illustrated in FIG. 4 and FIG. 5 is substantially the same as the above-mentioned configuration in the first embodiment. In this embodiment, plural grooves 17 extended from the rotating shaft 11 side to the through holes 15 are formed along the inner surface of the hub 14. In addition, as illustrated in FIG. 6, the grooves 17 and the through holes 15 are located between the position of the outside diameter R_(h) of the hub 14 and the position of the outside diameter R_(sh) of the shroud 13 of the vanes 12.

In the configuration of this embodiment, a working fluid sucked from a suction port (located on the left side of FIG. 4) by the rotation of the impeller 10 is increased in speed and pressure by the centrifugal action of the impeller 10. The working fluid is then guided to the downstream side. The liquid that flowed into the impeller 10 is about to attach to the hub 14 but the liquid is smoothly guided to the through holes 15 through the grooves 17 located between the position of the outside diameter R_(h) of the hub 14 and the position of the outside diameter R_(sh) of the shroud 13 and then the liquid is efficiently discharged to the rear side of the impeller 10 through the through holes 15. This makes it possible to prevent the liquid from attaching to the vanes 12 and suppress degradation in the efficiency due to increase in the shaft power of the impeller 10.

Therefore, by forming the plural through holes 15 penetrating the hub 14 from the front side to the rear side of the impeller 10 and the grooves 17 extended from the rotating shaft 11 side to the through holes 15 as in this embodiment, even when the centrifugal compressor 1 is operated in an environment in which the liquid is mixed, droplets that entered the impeller 10 can be efficiently removed and the compressor 1 can be operated without degrading the efficiency of the impeller 10 or narrowing the operating range thereof.

Third Embodiment

FIG. 7 illustrates a centrifugal compressor 1 according to a third embodiment of the present invention.

The configuration of the centrifugal compressor 1 according to this embodiment illustrated in FIG. 7 is substantially the same as the above-mentioned configuration in the first embodiment. In this embodiment, the impeller 10 includes on the rear side a leakage reducing member 16 for reducing a leakage flow flowing back from the outlet of the impeller 10 to the through holes 15. This leakage reducing member 16 may be provided in the centrifugal compressor 1 according to the second embodiment.

The above-mentioned leakage reducing member 16 includes a protruded portion 14A protruded in the axial direction from the rear side (right side of FIG. 7) of the hub 14 and an unevenness portion 18A formed in a part of the casing 18 to face the protruded portion 14A. The protruded portion 14A and the unevenness portion 18A form a sealing portion.

In the configuration in this embodiment, the liquid that entered the impeller 10 is about to attach to the hub 14 but almost all the droplets are discharged to the rear side of the impeller 10 through the through holes 15 located between the position of the outside diameter R_(h) of the hub 14 and the position of the outside diameter R_(sh) of the shroud 13. This makes it possible to prevent the liquid from attaching to the vanes 12 and suppress degradation in the efficiency due to increase in the shaft power of the impeller 10. In addition, owing to the leakage reducing member 16 provided on the rear side of the impeller 10, it is possible to reduce a leakage flow flowing back from the outlet of the impeller 10 to the through holes 15. Therefore, it is possible to suppress degradation in the efficiency of the impeller 10.

Therefore, by forming the plural through holes 15 penetrating the hub 14 from the front side to the rear side of the impeller 10 and the leakage reducing member 16 for reducing a leakage flow flowing back from the outlet of the impeller 10 to the through holes 15 as in this embodiment, even when the centrifugal compressor 1 is operated in an environment in which the liquid is mixed, droplets that entered the impeller 10 can be efficiently removed and the compressor 1 can be operated without degrading the efficiency of the impeller 10 or narrowing the operating range thereof.

The present invention is not limited to the above-mentioned embodiments and includes various modifications. For example, the above embodiments are described in detail in order to make the present invention easy to understand and the invention is not necessarily limited to the embodiments provided with all the configuration elements described herein. Some configuration elements of an embodiment may be replaced with or added to configuration elements of another embodiment. In addition, with respect to each embodiment, some configuration elements thereof may be added to, deleted from, or replaced with other configuration elements thereof.

EXPLANATION OF REFERENCE CHARACTERS

1 . . . Centrifugal compressor

10 . . . Impeller

11 . . . Rotating shaft

12 . . . Vane

13 . . . Shroud

14 . . . Hub

14A . . . Protruded portion

15 . . . Through hole

16 . . . Leakage reducing member

17 . . . Groove

18 . . . Casing

18A . . . Unevenness portion 

1. A centrifugal compressor comprising: a rotating shaft which rotates rotationally; and an impeller including a hub fixed to the rotating shaft and a plurality of vanes fixed to the hub at a predetermined interval in a circumferential direction; wherein the centrifugal compressor compresses a fluid by rotation of the impeller, and wherein the hub includes a plurality of through holes penetrating the hub from a front side to a rear side of the impeller.
 2. The centrifugal compressor according to claim 1, wherein the through holes are provided between the vanes on the rotating shaft side.
 3. The centrifugal compressor according to claim 1, wherein the through holes are located between an inlet radius Rh of the hub and an inlet radius Rsh of a shroud of the vanes.
 4. The centrifugal compressor according to claim 1, wherein a plurality of grooves extended to the through holes are formed along an inner surface of the hub.
 5. The centrifugal compressor according to claim 4, wherein the grooves and the through holes are located between an inlet radius Rh of the hub and an inlet radius Rsh of a shroud of the vanes.
 6. The centrifugal compressor according to claim 1, wherein the impeller includes a leakage reducing member on the rear side, the leakage reducing member reducing a leakage flow flowing back from an outlet of the impeller to the through holes.
 7. The centrifugal compressor according to claim 6, wherein the leakage reducing member includes a protruded portion protruded in a axial direction from a rear side of the hub and an unevenness portion formed in a part of a casing to face the protruded portion, and wherein the protruded portion and the unevenness portion form a sealing portion. 